The invention concerns a process for producing a marking, for example digits, letters, surface patterns, surface images or decoration, on a substrate, preferably a film, in particular a transfer film, wherein energy in the form of radiation, preferably laser radiation, is introduced from a controllable energy source into a replication surface of a replication apparatus to produce at least one shaping region and wherein the shaping region of the replication surface is shaped on to the substrate by the replication apparatus contacting the substrate under pressure, and an apparatus for producing a marking, for example digits, letters, surface patterns, surface images or decoration on a substrate, preferably a film, in particular a transfer film, comprising a replication apparatus which has a replication surface, a device for producing a radiation, preferably a laser installation, wherein the radiation is directed on to at least one portion of the replication surface to produce at least one shaping region, and a counterpressure apparatus which has a counterpressure surface, wherein the substrate is arranged between the replication surface of the replication apparatus and the counterpressure surface of the counterpressure apparatus in order to shape the shaping region on to the substrate in a contact region between the replication surface and the substrate.
The protection of documents by security features has in the meantime become a standard in the case for example of credit cards, personal identity cards or banknotes. The forgery-proof nature of those features is based on the fact that a high level of special knowledge and extensive apparatus equipment is necessary for the production thereof. A particularly successful security feature which is difficult to copy is an optical variable device. Embodiments of that security feature have diffractive or holographic structures which, upon a change in the angle of incidence of light or the viewing angle, during visual checking of the authenticity of the security feature, lead to an optical effect such as for example a color change, a motif change or a combination of the two. The security feature can thus be checked for its authenticity without further technical aids. An essential component part of those security elements is a generally thermoplastic or UV-hardenable layer into which the diffractive or holographic structure is embossed in the form of a surface relief. That layer can be part of a transfer film, in which case the security element is produced first and thereafter transferred on to the document to be safeguarded. That layer can also be provided in the form of an additional layer directly on the article to be safeguarded. Rotating stamping cylinders as are described for example in EP 0 419 773 or stamping punches as are disclosed for example in DE 25 55 214 are used for transferring the surface relief from a mold on to the thermoplastic layer. Production of the mold is technically very demanding and also cost-intensive by virtue of the fine diffractive or holographic structures. To manufacture the molds firstly patterns, also referred to as masters, are produced for example by interfering laser beams and etching processes or by electron beam writing, which are then generally galvanically shaped.
In the case of the known processes, for enhanced forgery-proof nature, the endeavour is that the same security feature is not applied to each document, but the security features are adapted to the respective document or to the identity of the owner of the document, that is to say individualised. In that respect two difficulties arise in the above-mentioned processes:
On the one hand a large number of individualised masters would have to be produced, which is highly cost-intensive, while secondly the molds have to be respectively interchanged in the replication apparatuses, which would result in very long equipment setting times. As alternatives, processes and apparatuses are known, which shape only partial regions of a mold in order to produce individualised security features.
CH 594 495 describes a process for stamping a relief pattern into a thermoplastic information carrier, wherein selectively only partial regions of the mold are shaped into the thermoplastic layer. In terms of process engineering, those shaping regions are selected by either those regions being heated by heating bands through which current flows, or by only the selected shaping regions being pressed on to the substrate by a counterpressure device which has partial regions which are adjustable in respect of height. A high level of local resolution in regard to selection of the shaping regions is not to be expected with that process as heat conduction during the long heating-up and cooling-down phase for the heating bands means that the boundaries of the shaping regions can be only inaccurately defined or the dimensions of the shaping regions are established by the dimensions of the bands or the dimensions of the partial regions which are adjustable in respect of height. That process is consequently limited by virtue of the fact that it involves a low level of local resolution.
EP 0 169 326 describes an apparatus for producing a marking on a substrate and the process corresponding thereto. The apparatus has a replication apparatus in the form of an unheated stamping mold and a pressure plate in the form of a counterpressure apparatus. The stamping mold has a replication surface which is structured with microstructures to be shaped. The apparatus has a laser arrangement for producing a laser beam which is directed on to the substrate through the counterpressure apparatus. The known process provides that firstly the substrate is pressed on to the pressure plate by the stamping punch. Due to absorption of the laser beam which is incident on the substrate directly in the stamping region, the substrate is selectively locally heated and raised to a temperature at which it can be durably permanently deformed. Positioning of the laser beam makes it possible in that way to selectively select and transfer shaping regions. A limitation with this process and apparatus is that the replication apparatus is in the form of a stamping punch. This means that the process is limited to a cyclic mode of processing, which is contrary to the attainment of a high level of productivity.